In response to industry demand, transmission and engine manufacturers continue to optimize the size of their transmissions and engines. Accordingly, transmission and engine manufacturers have required smaller components from their suppliers. The imposition of smaller spatial constraints has introduced a number of challenges to suppliers of transmission and engine components, particularly in the area of filtration.
In many cases, spatial constraints have reduced the available footprint for a powertrain filter. The reduced filter footprint has reduced the available filter media surface area inside the filter. In some cases, the reduced surface area provided by conventional filter media and filter designs has introduced a number of problems including maintaining a low pressure differential across the filter during cold start-up as well as during high temperature operating conditions. As one skilled in the art will readily appreciate, maintaining a low pressure differential across the filter during cold start facilitates quick priming of the fluid pump. As one skilled in the art will also appreciate, maintaining a low pressure differential across the filter during hot operation prevents pump cavitation.
One approach to providing a low pressure differential across a filter, given a limited packaging space, has been to use less efficient filtration media. Less efficient media is less restrictive, which permits fluids to pass through the media more freely, resulting in a lower pressure differential. One drawback to this approach, however, is that using filter media that is less efficient allows larger contaminants to pass through the filter. Allowing larger contaminants to pass through the filter media is not desirable because the presence of large contaminants in the system may lead to poor shift quality or premature failure of the transmission. Another drawback to this approach is that as the filter gets smaller, the available media area also reduces causing the velocity through the media to increase resulting in lower filtration efficiency.
Another approach to providing a low pressure differential across a filter given a limited surface area has been to increase the surface area of the filter media by using it in a non-planar configuration. The most predominant non-planar media configuration that substantially improves surface area is pleating. Pleating the filter media provides a greater surface area than filter media used in a conventional bag or single layer filter configuration. The increased surface area of the filter media serves to lower the pressure differential across the filter media. One of the drawbacks to prior filter design approaches using pleated filter media is that these designs are expensive. Prior pleated filter designs have been more expensive to manufacture than a conventional transmission filter. One prior design approach requires several plastic joining operations whereas the manufacturing process for a conventional filter having media in single layer or bag format may only require one plastic joining or metal crimping operation. For example, one design of prior pleated filters requires a separate manufacturing process to form the filter media into pleats by creating a pleat-pack by way of over-molding or urethane casting. Once a pleat pack has been manufactured, the pleat pack is joined in a first plastic joining operation to a first cover and then joined to a second cover in a separate plastic joining operation. Another drawback to pleated existing non-planar media configurations is that they hold the media in a “saw-tooth” configuration in which the fluid cross-section, in the direction of fluid flow, decreases along the pleat until reaching a line at the apex of the pleat. This reduction in fluid flow area results in a higher pressure differential than would be provided by gradually reducing fluid cross-section as would be provided by more of a “trapezoidal wave” or sinusoidal non-planar fold media configuration. Some designs that make use of standard pleats hold the filter media folded at a very tight angle, perhaps as small as 15°. In such a design, the initial pleating operation may damage the media at the outset. Another drawback of such a design is that by holding the media at tight angles under high fluid velocities may result in media damage and cause lower filtration efficiency.
Accordingly, it is desirable to provide a transmission filter with a sufficiently low pressure differential across filter media within given spatial constraints without reducing the efficiency of the filter media, thereby permitting large contaminants to pass through the filter. It is also desirable to provide a transmission filter design with adequate filter media surface area without incurring the manufacturing expense or design drawbacks of prior pleated filter designs.